N-(phosphonomethyl)glycine is described by Franz in U.S. Pat. No. 3,799,758. N-(phosphonomethyl)glycine and its salts are conveniently applied as a post-emergent herbicide in an aqueous formulation. It is a highly effective and commercially important broad-spectrum herbicide useful in killing or controlling the growth of a wide variety of plants, including germinating seeds, emerging seedlings, maturing and established woody and herbaceous vegetation, and aquatic plants.
One of the more widely accepted methods of making N-(phosphonomethyl)glycine compounds comprises oxidatively cleaving a carboxymethyl substituent from an N-(phosphonomethyl)iminodiacetic acid substrate. Over the years, a wide variety of methods have been disclosed for conducting this oxidation. See generally, Franz, et al., Glyphosate: A Unique Global Herbicide (ACS Monograph 189, 1997) at pp. 233-62 (and references cited therein); Franz (U.S. Pat. No. 3,950,402); Hershman (U.S. Pat. No. 3,969,398); Chou (U.S. Pat. No. 4,624,937); Chou (U.S. Pat. No. 4,696,772); Ramon et al. (U.S. Pat. No. 5,179,228); Felthouse (U.S. Pat. No. 4,582,650); Siebenhaar et al. (PCT/EP99/04587); and Ebner et al. (International Publication No. WO 99/43430). Although many of these processes produce suitable yields of various N-(phosphonomethyl)glycine products, a need continues to exist for an improved process for oxidizing N-(phosphonomethyl)iminodiacetic acid substrates. Desirable improvements include increased throughput, reduced cost per unit of N-(phosphonomethyl)glycine product, and reduced concentrations of undesirable by-products (e.g., formaldehyde, formic acid, N-methyl-N-(phosphonomethyl)glycine (NMG), and aminomethylphosphonic acid (AMPA)).